Capacitive touch sensor

Abstract

A capacitive touch sensor includes a touch interface, a switch, and a sensing circuit. The switch circuit switches based on sensing conditions of self-capacitance and mutual capacitance. The sensing circuit is used for both the self-capacitance mode and the self-capacitance mode to simplify circuit structure and save circuit area and power consumption. The output sensing voltage from the sensing circuit is stable. A differential mode is designed to improve noise interference and enhance accuracy of judging the touch effect. Then, the self-capacitance mode is utilized for the areas of possible touches to save operation time for the capacitance mode.

What is claimed is: 
     
       1. A capacitive touch sensor, comprising:
 a touch interface having first lines and second lines; 
 a first switch circuit connected between the first lines and a mutual capacitance voltage; 
 a second switch circuit, connected with the first lines and the second lines, for receiving a self-capacitance voltage and generating a sensing input voltage; and 
 a sensing circuit for receiving the sensing input voltage and generating a sensing output voltage, 
 wherein the second switch circuit comprises second switch units, each including:
 a self-capacitance voltage switch connected between the self-capacitance voltage and the touch interface; 
 a first sensing switch connected between the touch interface and output terminals of the switch units; and 
 a second sensing switch connected between output terminals of the switch circuits and adjacent switch unit. 
 
 
     
     
       2. The capacitive touch sensor according to  claim 1 , wherein the first switch circuit comprises at least a first switch unit connected between the first lines and the mutual capacitance voltage. 
     
     
       3. The capacitive touch sensor according to  claim 1 , wherein the second switch unit further comprises a second self-capacitance switch connected between a second self-capacitance voltage and the touch interface. 
     
     
       4. The capacitive touch sensor according to  claim 3 , wherein the sensor is provided with:
 a mutual capacitance mode, in which the first switch circuit conducts the first switch units sequentially and provides the mutual capacitance voltage to the first lines whereas the second switch units conduct the first sensing switch and turn off the self-capacitance voltage switch, the second sensing switch and the second self-capacitance switch; and 
 a self-capacitance mode, in which the first switch units are turned off, the second switch units conduct the first sensing switch or the second sensing switch based on channel scan, the self-capacitance voltage switch or the second self-capacitance switch is conducted based on operation timing of the sensing circuit, and the self-capacitance voltage or the second self-capacitance voltage is provided to the second lines or the first lines. 
 
     
     
       5. The capacitive touch sensor according to  claim 4 , wherein the self-capacitance mode is executed first to determine whether there are any self-capacitance sensing values in the first lines exceeding a predetermined range, and then the mutual capacitance mode is executed to carry out mutual capacitance scan for the first lines having self-capacitance sensing values exceeding the predetermined range and ignore the rest of the first lines. 
     
     
       6. The capacitive touch sensor according to  claim 4 , wherein the self-capacitance mode comprises:
 an odd mode, in which the first sensing switch and the second sensing switch in the odd-numbered second switch units are conducted, the self-capacitance voltage switch is conducted based on operation timing of the sensing circuit, and the second self-capacitance switch is turned off; and the first sensing switch and the second sensing switch in the even-numbered second switch units are turned off, the second self-capacitance switch is conducted based on operation timing of the sensing circuit, and the self-capacitance voltage switch is turned off; and 
 an even mode, in which the first sensing switch and the second sensing switch in the even-numbered second switch units are conducted, the second self-capacitance switch is conducted based on operation timing of the sensing circuit, and the self-capacitance voltage switch is turned off; and the first sensing switch and the second sensing switch in the odd-numbered second switch units are turned off, the elf-capacitance voltage switch is conducted based on operation timing of the sensing circuit, and the second self-capacitance switch is turned off. 
 
     
     
       7. The capacitive touch sensor according to  claim 4 , wherein the sensing circuit comprises one or more sensing units; when there is only one sensing unit, the first sensing switch or the second sensing switch in the second switch units are sequentially conducted during scanning to obtain a sensing output voltage from each of the first line or the second line; and when there are more than one sensing unit, the second switch units have out terminals connected to the sensing units to conduct the first sensing switch or the second sensing switch, thereby obtaining sensing output voltages from the sensing units. 
     
     
       8. The capacitive touch sensor according to  claim 7 , wherein the sensing unit comprises:
 a first amplifier having a positive input terminal connected to a reference voltage and a negative input terminal connected to an output terminal of the switch circuit, the negative input terminal and the output terminal of the first amplifier being connected with a first capacitor and a first timing switch; and 
 a second amplifier having a positive input terminal connected to the reference voltage and a negative input terminal connected to the output terminal of the first amplifier through a first resistor and a second timing switch, the negative input terminal and an output terminal of the second amplifier being connected with a second capacitor and a third timing switch; and 
 wherein the output terminal of the second amplifier is used for output of the sensing circuit. 
 
     
     
       9. The capacitive touch sensor according to  claim 8 , wherein the sensing unit further comprises a third amplifier having a positive input terminal connected to the reference voltage and a negative input terminal connected to the first resistor through a second timing negative switch, the negative input terminal and an output terminal of the third amplifier being connected with a second negative capacitor and a third timing negative switch; and wherein the output terminal of the third amplifier is used for negative output of the sensing circuit. 
     
     
       10. The capacitive touch sensor according to  claim 9 , in which:
 the first timing switch of the sensing unit is conducted at a first timing, and the self-capacitance voltage switches in the second switch units are additionally conducted in the self-capacitance mode; 
 the second timing switch or the second timing negative switch of the sensing unit is conducted at a second timing; and 
 the third timing switch or the third timing negative switch of the sensing unit is conducted at a third timing. 
 
     
     
       11. The capacitive touch sensor according to  claim 8 , wherein the sensing unit is connected with a switching circuit for receiving at least two voltages among the sensing output voltage, the sensing output voltage of the adjacent sensing unit and the reference voltage, and outputting a switching circuit positive output voltage and a switching circuit negative output voltage, and is provided with at least one of the following modes:
 a first switching mode, in which the sensing output voltage of the sensing unit and the sensing output voltage of the adjacent sensing unit are selected as the switching circuit positive output voltage and the switching circuit negative output voltage, respectively; and 
 a second switching mode, in which the sensing output voltage of the sensing unit and the reference voltage are selected as the switching circuit positive output voltage and the switching circuit negative output voltage, respectively. 
 
     
     
       12. The capacitive touch sensor according to  claim 9 , wherein the sensing unit sends a sensing negative output voltage to a switching circuit for receiving at least two voltages among the sensing output voltage, the sensing negative output voltage, the sensing output voltage of the adjacent sensing unit, the sensing negative output voltage of the sensing unit, and the reference voltage, and for outputting a switching circuit positive output voltage and a switching circuit negative output voltage, and is provided with at least one of the following modes:
 a first switching mode, in which the sensing output voltage of the sensing unit and the sensing output voltage of the adjacent sensing unit selected as the switching circuit positive output voltage and the switching circuit negative output voltage, respectively; 
 a second switching mode, in which the sensing output voltage of the sensing unit and the reference voltage are selected as the switching circuit positive output voltage and the switching circuit negative output voltage, respectively; 
 a third switching mode, in which the sensing negative output voltage of the sensing unit and the sensing negative output voltage of the adjacent sensing unit are selected as the switching circuit positive output voltage and the switching circuit negative output voltage, respectively; and 
 a fourth switching mode, in which the sensing negative output voltage of the sensing unit and the reference voltage are selected as the switching circuit positive output voltage and the switching circuit negative output voltage, respectively. 
 
     
     
       13. The capacitive touch sensor according to  claim 11 , further comprising an analog/digital converter for receiving voltages from the sensing circuit and the switching circuit and outputting a digital signal. 
     
     
       14. The capacitive touch sensor according to  claim 4 , wherein each of the first lines or the second lines in the touch interface is connected with a reference capacitance switch having another end connected to a reference capacitor applied with a mutual capacitance second voltage; and the reference capacitance switches are conducted in the mutual capacitance mode and turned off in the self-capacitance mode.